1. Field of the Invention
This invention relates to an alkali-developable black photosensitive resin composition for forming a light-shielding barrier wall having a height of not less than 20 μm by photolithography, its cured product, and a light-shielding barrier wall formed from the cured product mentioned above. More particularly, the present invention relates to a black photosensitive resin composition for forming black matrices of a liquid crystal display device, an electronic display device, etc. and light-shielding barrier walls etc. of optics which are used for image transmission devices for writing optical systems of an optical printer etc. or reading optical systems of a scanner, a copying machine, etc.
2. Description of the Prior Art
In recent years, in view of the demand for miniaturizing the electronic equipment, the miniaturization of parts used for them is indispensable. In addition thereto, high resolution is required for the image transmission devices for writing optical systems, such as an optical printer, and for reading optical systems, such as a scanner. Heretofore, a gradient index rod lens array has been used for imaging optical systems used in these image transmission devices. According to this gradient index rod lens array, a very compact erect equal-magnification imaging optical system can be realized. However, since this lens array is produced by arranging many rod lens elements and fixing them with a resin, it tends to generate unevenness of the arrangement of rod-lens elements. Such uneven arrangement had affected the resolution of the lens array and became the cause of generating unevenness of picture in the high-resolution equipment.
As a lens array which can suppress occurrence of such uneven arrangement, a resin erect lens array has been developed recently. A resin erect lens array realizes an erect equal-magnification imaging optical system by laminating two or more flat lens array plates having many lenses formed in the surface of a transparent substrate. Although such a resin erect lens array has been heretofore used in combination with a liquid crystal display element to create a liquid crystal image in a space or on an object. In order to apply a resin erect lens array to an optical printer or a scanner, however, it is necessary to improve resolution and an amount of transmitting light and to reduce the stray light.
In order to reduce the unevenness of arrangement or the stray light in these erect equal-magnification imaging optical systems, it is desirable to form light-shielding portions in the recesses between lenses so that the light collected with the lenses is efficiently transmitted. As a method for forming light-shielding portions to be used in an erect equal-magnification imaging optical system, a method of interposing a sheet of light-shielding film between lens plates (see JP 2004-070268, A) and a method of pouring black ink into the recess between lenses (see JP 2003-202411, A), for example, have so far been devised. However, both methods have the problems in workability and the reproducibility of openings.
On the other hand, in a color filter to be used for a display material in a liquid crystal display, an electronic display, or the like, a thin film of black matrix of several μm thickness is formed between fine pixels colored at least two or more of hues for the purpose of intercepting light and raising contrast and in order to prevent a decrease in the intensity of color. This black matrix is generally formed by photolithography which comprises the steps of applying a composition containing a photosensitive prepolymer and a pigment, such as carbon black, directly added thereto, onto a glass substrate, exposing the resultant coating film to light according to a prescribed pattern, and then performing development. Since the photolithography is suitable for mass production owing to the good workability, it is widely used in the printing industry or the electronics industry still now.
However, such a composition aiming at the light-shielding requires a light-shielding black pigment, such as carbon black, to be contained in the composition in a large amount to make the composition black. Therefore, in photolithography it sustains remarkable underexposure and tends to attain insufficient curing depth. As a result, there are such problems that the undercutting will be easily produced in a developing process and that the adhesiveness to a substrate will be inferior. That is, it will be hardly possible to perform the patterning of a film having the thickness of not less than 20 μm, particularly the thickness in the range of 50 μm to 100 μm, by the photolithography with sufficient degree of blackness because of insufficient curing property in a deep portion of a coating film. Further, If an exposure dose is increased in the step of exposure to light for the purpose of improving the curing property in a deep portion, there is such a problem that halation will become large and the resolution will decrease in proportion to the increase of the exposure dose. Therefore, at present there is no black photosensitive resin composition which is capable of coping with the thick film and forming a film of sufficient degree of blackness having the thickness of not less than 20 μm without causing the undercutting during development.